In the prior art, asset management systems are known which are based on RFID technology. The core of such a system is the transponder or RFID tag. Such a transponder can be attached to, or embedded, in an object. The transponder is provided with a memory for storing data relating to the object.
In an RFID system, an RFID reader is used, which sends out a radio frequency signal to the transponder. This signal is received by a transponder which, in reply to this signal, sends back the data stored in the memory, on the transponder to the reader.
The RFID system uses two separate antennas. One antenna is present on the transponder and the second antenna is present on the reader. The antenna on the reader is used to send out a power pulse which can be received by the antenna on the RFID transponder. This power pulse is used to activate the transponder. After the reception of the power pulse, the RFID transponder is able to reply by transmitting the data stored on the RFID transponder using its own antenna.
The data transmitted by the RFID transponder can either be transmitted directly to another system like a host computer, through standard interfaces, or can be stored in a portable reader to be uploaded later to a computer for data processing. The advantage of using RFID transponders is the fact that RFID system works effectively in environments with excessive dirt, dust, moisture and/or poor visibility.
In the prior art, different kinds of RFID transponders are available. A first group of RFID transponders are “passive transponders”. These passive RFID transponders do not require the presence of a power source, like a battery for electronic circuits supplying. Generally, they are powered by the reader using an induction mechanism.
According to this principle, an electro-magnetic field is emitted by the reader antenna and received by the antenna located on the RFID transponder. The reader sends out a power pulse of, for instance, 134.2 KHz. This power pulse is collected by the antenna in the passive RFID transponder that is tuned to the same frequency. This received AC energy is rectified and stored on a small capacitor within the RFID transponder. When the power pulse has finished, the RFID transponder immediately transmits back its data, using the energy stored within the capacitor as its power source.
Generally, 128 bits are transmitted over periods of 20 ms. This transmitted data is picked up by the receiving antenna positioned in the reader and the data are decoded by the reader. Once all the data have been transmitted, the storage capacitor on the RFID transponder is discharged, resetting the transponder to make it ready for a next reading cycle. The period between transition pulses is known as the “SYNC TIME” and lasts between 20 ms and 50 ms, depending on the system set up. The transmission technique used between the RFID and the reader is FREQUENCY SHIFT KEYING (FSK) with the transmission generally comprised between 124.2 Kz and 134.2 Kh. An important advantage of the passive RFID transponders is their price. Passive RFID tags have typically a price per unit of 0.3 euros. An important disadvantage of the use of passive RFID transponders is the fact that they have a limited range, typically less than one meter.
A second type of RFID transponders are the so-called “active RFID transponders”. Active RFID transponders are provided with a power source, such as a battery, to supply the electronic circuits and to enhance the transmittal of data from the transponder towards a reader. An important advantage of the presence of such a power source is the fact that active RFID transponders typically have a range of 20-30 meters. A drawback of the use of active RFID transponders is their unit price of about 10 euros. Active RFID tags are too expensive to use on individual products. In practice, the use of active RFID transponders is therefore limited to, for instance, pallets and boxes.
In order to use RFID technology for example in an asset management system, an RFID transponder is attached to each item in a storage area. The information on the RFID transponders on those products is read by means of an associated RFID reader. In order to make such an asset management system affordable, it appears to be preferable to use the inexpensive passive RFID tags. However, because of the limitation of the reading range of these passive RFID tags, such an asset management system requires an expensive reader infrastructure. For instance, in order to locate a given item within a set of shelves, a plurality of readers will have to be present in a storage area, wherein each reader uses several channels associated with several antennas. This reader infrastructure in itself is not only expensive but also difficult to install in a storage area and difficult to manage.
In case a rather simple reader infrastructure is preferred, the items in the storage area will have to be provided with an active RFID tag in order to allow communication between the products and the rather distant reader. Because of the high price per unit of the active RFID transponders, the use of active RFID transponders the products in combination with a limited reader infrastructure will lead to an even more expensive asset management system.
In the light of the disadvantages of the present RFID technology, an aim of the invention is to overcome some or all these limitations by means of an asset management system which allows a relatively simple reader infrastructure and the use of relatively inexpensive RFID transponders.